Various chemicals used today are transferred from supply tanks to smaller usable tanks by means of a flexible hose. The supply tank usually has a manual tank valve which controls the flow into the hose and the hose usually has a flow control nozzle valve for a temporary shutoff.
Various chemicals such as anhydrous ammonia which is shipped under a concentrated condition are transferred from a supply tank to a smaller container for transport and use. When the manual tank valve is shut off and the nozzle control valve is shut off, a small amount of concentrated gas is trapped within the hose. Over a period of time, if the hose is allowed to remain in the sun or under a heated condition, the gas will expand, creating excessive pressure upon the hose which may cause the hose to burst. Chemicals such as anhydrous ammonia or the like are highly dangerous when inhaled or can be dangerous to skin contact and flying debris is hazardous to personnel. Therefore an exploding hose would create an undue hazard to transfer operators.
Other safety valves vent the excessive gas from the hose into the surrounding atmosphere exposing personnel to the hazardous gas.